In recent years, fine particles in nanometer order are considered for application to various devices. For example, metal fine particles of nickel are used for a ceramic capacitor at present, and fine particles with a particle diameter of 200 nanometers or less having good dispersibility are considered to be used for a next generation ceramic capacitor.
Furthermore, fine particles of silicon monoxide (SiOx:x=1 to 1.6) having a lower oxygen content than silicon, dioxide are utilized as an antireflection film of an optical lens or a deposition material of a gas-barrier film for food packaging. Recently, application of the fine particles to an anode material of a lithium-ion secondary battery is expected.
As a common method of producing fine particles in nanometer order, there are a method of introducing a bulk material as a raw material together with beads such as ceramic beads and zirconia beads, and miniaturizing the material into particles by mechanical crushing, a method of melting and evaporating a material and spraying the material to air or water to obtain fine particles and a method of chemically obtaining fine particles by electrolysis or reduction, etc. Among them, a method of producing fine particles in a vapor by using thermal plasma (approximately 10000° C.) such as high-frequency plasma or arc plasma is extremely useful because the produced fine particles are excellent in dispersibility with less contamination and composite fine particles formed of plural kinds of materials can be easily composed (for example, refer to JP-A 2004-263257 (Patent Document 1)).
FIG. 4 shoves a schematic cross-sectional view of a production apparatus for fine particles utilizing thermal plasma according to a related art example 1.
A powder generator 101 has a hollow body, which is roughly divided into a fine mist introduction part 201, a fine mist reservoir part 202 and a reaction part 203. The fine mist introduction part 201 is provided to be directed to the fine mist reservoir part 202 on a side in a lower part of the powder generator 101, and the cylindrical reaction part 203 continues above the fine mist reservoir part 202. A powder collection part 204 includes a filter member thereinside, for example, a bag filter 205 for separating fine particles and the gas. A suction machine 206 is provided to suck inside the powder generator 101 through a duct 207, the bag filter 205 inside the powder collection part 204 and a duct 208, discharging the gas passing through the bag filter 205 to the outside. The reaction part 203 includes a group of electrodes 210, and these electrodes 210 are connected one by one to secondary-side terminals of respective phases in a polyphase AC converter 211 which converts three-phase alternating current supplied from a commercial power supply into polyphase alternating current through plural single-phase transformers. Moreover, tip end portions of the electrodes 210 are positioned around an axial center of the reaction part 203 at equal intervals, which are arranged so that phase differences between adjacent tip end portions are equal to one another, thereby forming a plasma 212 among the electrodes 210. Fine mist is allowed to pass through the plasma 212 to generate fine particles, which can be collected by the bag filter 205 of the powder collection part 204.